The present invention relates to an apparatus for manufacturing a thin film by sputtering, and more particularly relates to a magnetron-type sputtering apparatus capable of controlling the speed of deposition of a thin film.
In a conventional sputtering apparatus, glow discharge is caused in a low-pressure atmosphere of argon or the like, and plasma ions are made to collide against a cathode target to dislodge atoms from the target, which are then deposited on a base plate facing the target. Particularly, in a magnetron sputtering apparatus, a magnetic field is generated which is substantially parallel to a cathode target and which perpendicularly intersects the electric field. In such an apparatus, the speed of deposition of the thin film is high, and damage to the base plate on which the film is deposited and a rise in the temperature of the plate are prevented. Due to these advantages, magnetron sputtering apparatuses have been widely used.
A conventional magnetron-type sputtering apparatus includes a magnetic field generator having a permanent magnet or an electromagnet disposed near the rear side of the cathode target.
A plural-cathode sputtering apparatus, with which a thin mixture film can be manufactured while the composition of the film is controlled, has recently been disclosed. FIG. 4 shows a schematic view of a major part of such an apparatus, in which targets 41A and 41B differing from each other in material are provided. Permanent magnets 42A and 42B corresponding in shape to the targets IA and IB are provided at the rear sides thereof with which tunnel-shaped closed magnetic fields Xa are generated on the front sides of the targets by the north and south poles of the magnets. At the time of sputtering discharge, plasma electrons are trapped in the tunnel-shaped closed magnetic fields and ionization is promoted in the plasma to increase the speed of sputtering. Substrates 6, on which the films are deposited, are disposed on a holder 7.
In a method of depositing thin mixture films each composed of mutuallY different stratified atomic layers, shutters 45A and 45B provided in front of the targets 41A and 41B are selectively opened and closed and the holder 7 is rotated to deposit the thin mixture films. Voltages applied to the targets 41A and 41B from target power supplies 44A and 44B are maintained at desired levels. However, since the depth of stratification of each layer of the thin mixture film is mechanically limited by the speed of opening and closing of the shutters 45A and 45B, it is impossible to deposit a thin mixture film having a period of stratification (stratification depth) of about 10 521 to several scores of 10 .ANG.. In other words, it is impossible to make the thickness of each layer of such a film smaller using such a method.
In another method of depositing thin mixture films, independent power supplies 44A and 44B are provided for the targets 41A and 41B, and the lengths of time of application of voltages to the targets from the power supplies are controlled independently of each other to selectively change the lengths of time of discharge on the targets. In the latter method, thin mixture films of optional stratification can be deposited by changing the lengths of time of application of the voltages to the targets 41A and 41B. However, changing the lengths of time of application of the voltages can lead to damage to the power supplies 44A and 44B, as will be described below in more detail.
When the voltages are applied to the targets 41A and 41B, the change in the impedance before the generation of the plasma is so large that a large surge current flows. Therefore, if the period of application and removal of the voltage is short, not only is an undesirable sputtering discharge disturbance caused by the transient surge current, but also various components of the power supplies 44A and 44B tend to overheat, leading to damage. For that reason, the period of application and removal of the voltages to the targets 41A and 41B is limited by the performance of the power supplies 44A and 44B, again preventing the deposition of a thin mixture film, having a period of stratification as small as 10 .ANG. to several scores of 10 .ANG..